For example, in some games you can press a button to toggle some kind of screen witch shows you the fps and other data.
A good example is Minecraft (you've probably heard of it)
When you press F3, it shows you the fps, the player coordinates and a whole load of other stuff of witch I don;t know what it means.
Here is an image:------V the FPS is right there

I don't need help with the drawing itself, but only with collecting the information. ;)